This invention relates to methods for determining the curve radius of a roadway wherein the difference in wheel speeds of at least two unpowered wheels of a vehicle is measured and the rate of yaw of the vehicle, and hence the radius of the curve, is determined therefrom.
When negotiating curves in a roadway, the driver of a motor vehicle regulates the vehicle speed according to the roadway curve radius, the roadway conditions and the weather conditions. Increasingly, however, modem motor vehicles are equipped with vehicle speed control systems as well as navigation systems so that it is desirable to obtain accurate information concerning the course and condition of the roadway. This information may then be made available to the speed control system and/or the navigation system in the form of relevant parameters. In this way, for example, the course of the roadway may be compared with roadway information in a stored map, thus substantially improving the accuracy of the navigation system.
Such systems assist the driver operating the motor vehicle, insofar as possible, thereby also enhancing traffic safety.
In this connection, European Published Application No. 84 91 09 discloses a method for prospective determination of the route course ahead of a motor vehicle for an automatic distance warning system. In this method a curve radius is measured from the difference between the wheel speeds of at least two driving wheels. Since the wheel speeds of the driving wheels depends not only on the vehicle speed but also on other factors such as wheel slip and roadway condition, the curve radius determined by this method results in an approximate value only.
Accordingly, it is an object of the present invention to provide a method for determining a roadway curve radius which overcomes disadvantages of the prior art.
Another object of the invention is to provide a method of determining a roadway curve radius that uses conventional vehicle components in a simple way to measure a roadway curve radius with considerably greater accuracy and is capable of taking other influences into account at the same time.
These and other objects of the invention attained by assigning a fixed rotational angle corresponding to a fixed number of pulse generator pulses for each wheel, measuring the aggregate of a series of wheel pulses over the assigned wheel angle determining a ratio of the aggregate pulses from the wheels of a pair on one axle, and determining the aggregate wheel slip and hence the curve radius of turning from the ratio.
By this method, which is easily realized, the curve radius or the roadway curvature can be determined with very high precision without requiring any additional external equipment.
The simplest way to select the constant rotational wheel angle is to select a constant number of rotational pulses since vehicles having ABS or ASR have rotational pulse transmitters on all wheels.
To enhance the precision of measurement, it is advantageous if, for example, an xe2x80x9coffsetxe2x80x9d equation of the times to generate the constant number of pulses are determined for all wheels before each measurement or at preassigned time intervals by forming a mean of the ratios of the measured times. Such an offset equation is helpful in compensating for variations due to roadway differences, different road conditions, or differences in tires. The mean is a measure of the error between the two wheels when traveling in a straight line and may be taken into account in calculating the curve radius.
To eliminate the influence of vehicle acceleration processes as a source of possible error, it is further advantageous if the starting times of the time measurement for each pair of wheels are synchronized.